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Abstract:

Method and systems to detect tampering in a physical article are
described herein. A method includes receiving, at a first point in time,
at least two response signals from at least one RF tag in a set of RF
tags associated with the physical article; forming a first response
signature for the physical article based on the received response
signals; receiving a second response signal from at least one other RF
tag in the set of RF tags associated with the physical article at a
second point in time; assessing a relative spacing between the RF tags
associated with the physical article has changed from the first point in
time to the second point in time; and determining tampering of the
physical article as a result of the spacing assessment.

Claims:

1-22. (canceled)

23. A method of detecting tampering of a physical article, the method
comprising: receiving, at a first point in time, at least two response
signals from at least one RF tag in a set of RF tags associated with the
physical article forming a first response signature for the physical
article based on the received response signals; receiving a second
response signal from at least one other RF tag in the set of RF tags
associated with the physical article at a second point in time; assessing
a relative spacing between the RF tags associated with the physical
article has changed from the first point in time to the second point in
time; and determining tampering of the physical article as a result of
the spacing assessment.

24. The method of claim 23, wherein at least one RF tag comprises: at
least two non-coplanar power coils; and a circuit connected to the
non-coplanar power coils, the circuit configured to detect at least one
electrical characteristic from at least two of the non-coplanar power
coils, and to transmit a RF tag code and an indication of the detected
electrical characteristics to a RF tag reader.

25. The method of claim 24, wherein the electrical characteristic is at
least one of power, current, and voltage.

26. The method of claim 24, wherein the electrical characteristic is the
same for each of the at least two non-coplanar power coils.

27. The method of claim 24, wherein the at least two non-coplanar power
coils comprise at least three non-coplanar power coils, at least three of
which are formed on orthogonal planes.

28. The method of claim 24, wherein power from each of the non-coplanar
power coils is used to provide power to the circuit.

29. The method of claim 24, wherein at least one of the RF tags is a
passive RF tag.

30. The method of claim 23, wherein the first response signature
comprises a three dimensional RF signature, and wherein the method
comprises determining an orientation of the physical article based on the
three dimensional RF signature.

32. The method of claim 23, wherein the first response signature depends
on the orientation of the RF tags relative to a directed electromagnetic
radiation.

33. The method of claim 23, wherein the first response signature depends
on the placement of the RF tags on the article.

34. The method of claim 23, wherein the first response signature depends
on the path of motion of the article.

35. A RF tag system, comprising: at least two RF tags, at least one of
the RF tags comprising at least two non-coplanar power coils; and a
circuit connected to the non-coplanar power coils, the circuit configured
to detect at least one electrical characteristic from at least two of the
non-coplanar power coils; a RF tag reader configured to: receive a RF tag
code and an indication of the detected electrical characteristics from
the circuit; and determine tampering of the physical article based on the
received RF tag code and at least one detected electrical characteristic.

36. The system of claim 35, wherein the electrical characteristic is at
least one of power, current, and voltage.

37. The system of claim 35, wherein the electrical characteristic is the
same for at least two non-coplanar power coils.

38. The system of claim 35, wherein the at least two non-coplanar power
coils comprise at least three non-coplanar power coils, at least three of
which are formed on orthogonal planes.

39. The system of claim 35, wherein power from at least one of the
non-coplanar power coils is used to provide power to the circuit.

40. The system of claim 35, wherein at least one of the RF tags is a
passive RF tag.

41. The system of claim 35, wherein all of the RF tags are passive RF
tags.

42. The system of claim 35, wherein the RF reader is configured to
determine a three-dimensional response signature for the physical article
based on at least two response signals from at least one of the RF tags.

[0003] The present invention relates to Radio Frequency (RF) tags and,
more particularly, to three dimensional RF tag signatures.

[0004] 2. Description of the Related Art

[0005] Radio Frequency tags, also known as Radio Frequency Identification
(RFID) tags use electromagnetic radiation to temporarily charge a
circuit, which may be programmed to wirelessly transmit a data code. If
the data transmitted by the circuit is received by an RF tag reader, it
is possible to determine that the RF tag is in the proximity of the RF
tag reader. By causing different chips to transmit different RF tag
codes, the identity of the RF tag may be determined, which will allow a
RF tag processing system interfaced with the RF tag reader to uniquely
place that RF tag in a particular place at a particular point in time.
Thus, by associating the RF tags with individual articles that are to be
tracked, it is possible to keep track of many different articles
electronically. RF tags may be used in many applications, and the number
of applications of RF tags has been increasing dramatically in the last
few years. For example, RF tags are used in retail establishments to keep
track of merchandise, in manufacturing to keep track of inventory, in
corporations for example in building access badges, and in many other
fields.

[0006] FIG. 1 shows an example RF tag. As shown in FIG. 1, a standard RF
tag 10 includes a coil 12 that will be used to capture electromagnetic
radiation to produce a current. As is well known, changing an
electromagnetic field relative to a coil will cause an electrical current
to flow in the coil. Thus, by modulating an electromagnetic field it is
possible to cause a current to be generated in the coil of an RF tag.
Where the coil 12 is connected to an electromagnetic circuit 14, and the
electrical current is used to power to circuit 14. The circuit may be
used for many different things, but generally is configured to transmit a
tag response including a tag code that may be read by a RF tag reader 20
(see FIG. 2). RF tags are well known, and many different types and
sizes/shapes of RF tags and circuits have been developed.

[0007] As shown in FIG. 2, in operation a RF tag reader 20 generates a
strong electromagnetic field 22 which will cause a current to be
generated in any RF tags within a given distance of the RF tag reader.
When an RF tag 10 comes into proximity of the RF tag reader 20, the RF
tag will generate the tag response 24 which may be sensed by the reader
20 if the tag is sufficiently close to the reader 20.

[0008] RF tags provide an indication of presence of the tag relative to
the reader, but generally do not provide an indication of where the RF
tag is located within the reader's field of view. While it is possible to
use an RF tag reader that has one or more directional antennas to help
determine the relative position of the RF tag, doing so reduces the
ability of the RF tag reader to detect the presence of RF tags outside of
the directional antenna beam.

[0009] Similarly, when an RF tag is associated with an article, for
example where RF tags are to be used to track boxes of merchandise or
luggage, sensing the presence of an RF tag will enable the reader to
determine the rough location of a particular article at that particular
point in time. The RF reader is not able however, to determine the state
of the article or whether the article has been damaged or altered since
the last time the RF tag presence was sensed. Accordingly, while RF tags
are very useful for tracking where articles are at particular points in
time, it would be advantageous to provide a way in which the RF tags
could provide additional information about the articles being tracked.

SUMMARY

[0010] Three dimensional RF tag signatures may be obtained from a three
dimensional RF tag or multiple two or three dimensional RF tags so that
information in addition to presence information may be obtained. In one
embodiment, a three dimensional RF tag having two or more power coils
disposed in non-coplanar planes, enables the coils to experience
different levels of excitation from an electromagnetic field associated
with the RF tag reader. This information may be transmitted along with
the RF tag response to enable the orientation of the RF tag relative to
the RF tag reader to be determined. In another embodiment, multiple RF
tags (either standard RF tags or three dimensional RF tags) may be used
on a given article and a response signature from the article as a whole
may be recorded. The three dimensional response signature thus collected
may be compared with previous versions of the response signature to
determine if the article has been altered.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Aspects of the present invention are pointed out with particularity
in the appended claims. The present invention is illustrated by way of
example in the following drawings in which like references indicate
similar elements. The following drawings disclose various embodiments of
the present invention for purposes of illustration only and are not
intended to limit the scope of the invention. For purposes of clarity,
not every component may be labeled in every figure. In the figures:

[0012] FIG. 1 is a functional block diagram an RF tag;

[0013]FIG. 2 is a functional block diagram of the interaction between an
RF tag reader and an RF tag;

[0014] FIG. 3 is a functional block diagram of an RF tag having three
non-coplanar power coils according to an embodiment of the invention;

[0015]FIG. 4 is a diagram showing the electrical interconnection of the
power coils an circuit of the RF tag of FIG. 3 in greater detail;

[0016] FIG. 5 is a diagram of an article having a plurality of RF tags;

[0017] FIG. 6 is a functional block diagram of an RF tag reader obtaining
a three dimensional signature from an article such as the article of FIG.
5;

[0018] FIG. 7 is a flow chart illustrating a process of determining a
relative orientation of an RF tag from a signature of a three dimensional
RF tag, such as the RF tag of FIGS. 3-4, according to an embodiment of
the invention;

[0019] FIG. 8 is a flow chart illustrating a process of comparing a three
dimensional RF tag signature from an article having a plurality of RF
tags, such as the article shown in FIGS. 5-6, with a previous signature
for the same article according to an embodiment of the invention; and

[0020] FIG. 9 is a functional block diagram of a computer system
configured to implement an RF tag processing system according to an
embodiment of the invention.

DETAILED DESCRIPTION

[0021] The following detailed description sets forth numerous specific
details to provide a thorough understanding of the invention. However,
those skilled in the art will appreciate that the invention may be
practiced without these specific details. In other instances, well-known
methods, procedures, components, protocols, algorithms, and circuits have
not been described in detail so as not to obscure the invention.

[0022] FIG. 3 illustrates an example of a RF tag having more than one
power coil, in which the power coils are not formed to be co-planar. By
using non-co-planar power coils, the several power coils will generate
different amounts of power when subjected to a directional
electromagnetic field. The chip may transmit a power coil value
indicative of the amount of power, current, voltage, or another
measurable quantity, that it received from each power coil in connection
with generating its tag response. These power coil values may be used by
the RF tag reader or RF tag processing system to deduce an orientation of
the RF tag relative to the RF tag reader.

[0023] In the embodiment shown in FIG. 3, the three dimensional RF tag 30
includes three power coils 12X, 12Y, and 12Z. The three power coils are
connected to the circuit 32 and provide power to the circuit. Although
the embodiment shown in FIG. 3 has three power coils, the invention is
not limited in this manner as two power coils or a larger number of power
coils may be used as well. Additionally, although the embodiment shown in
FIG. 3 has the power coils disposed on orthogonal planes, this is merely
a preferred embodiment. The invention is not limited to this particular
embodiment as other types of three dimensional RF tags having more than
one power coil disposed in a non-planar fashion may have the power coils
disposed on differently oriented planes.

[0024]FIG. 4 provides additional details about how the power received
from the several power coils is used by the circuit 32. As shown in FIG.
4, the power received from each of the power coils 12X, 12Y, and 12Z is
added together to form an input power to the circuit 32. Additionally,
the electrical signals from the power coils 12X, 12Y, and 12Z are each
measured by the RF tag. The RF tag may measure the power from the power
coils, the amount of current being generated, the voltage, or another
electrical characteristic derivable from measuring the output of the
power coils.

[0025] Once the RF tag has taken measurements of the power coils, it will
transmit the tag code 34 along with power coil values to the RF tag
reader via an antenna 36. The power coil values are indications of the
electrical characteristics of the several power coils and may be actual
readings of the characteristic that is being measured, or one or more
values derived from the measured characteristic. The tag code may be a
standard tag code, and the rest of the circuit that is configured to
actually transmit the data may be the same as a standard RF tag, except
that instead of transmitting only a tag code the RF tag will also
transmit the power coil values as well.

[0026] The amount of current generated in a given coil depends not only on
the strength of the electromagnetic field, but also on the orientation of
the coil relative to the field. If a RF tag reader is transmitting
electromagnetic (EM) radiation, the direction of the radiation over the
area occupied by the three dimensional RF tag may be considered to be
relatively constant in one direction, given the size of a typical RF tag
relative to the distance to the RF tag reader. By placing the power coils
in different planes such as the orthogonal planes shown in FIGS. 3 and 4,
the power coils will therefore be oriented at different angles relative
to the EM radiation source. Thus, different currents should be produced
in each of the power coils of the RF tag. If the tag has a known
geometry, such as if the tag is formed to have three power coils on three
mutually orthogonal planes as shown in FIGS. 3 and 4, the orientation of
the tag relative to the reader may be determined.

[0027] The amount of current generated in a given coil may be expected to
be dependent on the strength of the EM field at the RF tag. If a point EM
source radiating in all directions is used to generate the EM field, then
the strength of the radiation should be expected to drop off on the order
of d3, where d is the distance from the point source to the RF tag.
By measuring the magnitude of the electrical response in these power
coils, a rough estimate of the distance between the RF tag and the tag
reader may be obtained.

[0028] The distance and/or orientation information obtainable from an RF
tag having multiple non-co-planar power coils may be used in many
different applications. For example, in manufacturing, a stationary RF
reader may use RF tags to identify when particular parts are approaching
a manufacturing station. Knowing the orientation of the RF tag may enable
the RF tag reader to determine if the part has been incorrectly placed on
the conveyance system, may help the RF tag reader to know where the part
is within its field of view, and may help in other ways. For example,
knowing the orientation of a tag may enable the system to know if the
article associated with the tag is up-side-down.

[0029] Similarly, where the location of the RF tag has been fixed and the
RF tag reader is mobile, knowing the direction from the reader to the RF
tag, and optionally the distance between the reader and the RF tag, may
help the RF tag reader stay on a desired side of the fixed RF tags. This
may be useful, for example in connection with self-propelled vehicles and
in other applications. For example, if the RF tags are embedded in a
roadway, the three dimensional signatures may enable an RF tag reader in
an automobile to know whether it is traveling on the left side or right
side of the RF tags.

[0030] The several example applications described herein are not intended
to limit application of the invention to one or two fields, but rather
have been provided to show some practical utility for the invention. The
invention is thus not limited to the use of the inventive three
dimensional RF tag signatures in these several applications, since the
signatures may be used in many different ways that are too numerous to
list herein.

[0031] Although an embodiment has been described in which multiple
antennas are connected to a given circuit, according to another
embodiment of the invention, multiple RF tags 10 associated with an
article may be used to generate a three dimensional signature for the
article. These RF tags may be conventional tags such as the tag shown in
FIG. 1, may be tags such as the RF tags discussed above in connection
with FIGS. 3 and 4, or may be differently configured RF tags. FIG. 5
shows one example of this where three RF tags 52 are placed at different
locations on an article 50. Since the RF tags will provide a spatial
signature for the article that is dependent on their position on the
article, changing the position of one or more of the RF tags will cause
the three dimensional signature for the article to change. Detecting a
change in the RF signature may thus enable a system to determine that the
article has been altered between readings. This may be useful, for
example, where security is an issue and it is important to detect whether
tampering has occurred. Similarly, although an embodiment will be
described in which the RF tags have been applied to an article, the
invention is not limited in this manner as the RF tags may also be
applied to a set of articles that are required to be kept together.

[0032] The signature will be unique to the article and depend on the
orientation of the RF tags, the placement of the RF tags, and possibly
the configuration of the article as well. For example, the RF tags may be
distributed to form a spatial signature for the article. The RF tags may
also be set to respond at different times so that the set of RF tags is
able to form a temporal signature. Similarly, the response of one or more
of the RF tags may be encoded, so that the signature is encoded. Thus,
the three dimensional signature may include spatial signatures, time
signatures, coding signatures, and combinations of these types of
signatures.

[0033] Once an initial three dimensional RF signature is received for a
given article, the signature may be stored for use at a later time. When
a new signature is received for the article, the new signature may be
compared with the stored signature to determine if the two signatures are
sufficiently alike. If the signatures are sufficiently similar, it may be
inferred that the RF tags or the relative placement of the RF tags has
not been disturbed. If the signatures are sufficiently dissimilar, it is
possible that the article has been tampered with, and an appropriate
notification may be provided.

[0034] The three dimensional signature provided by a set of RF tags
disposed within a given volume may be used in many different
applications. For example, a signature may be obtained from a box of
items. If the signature changes, it may be that the box has been opened.
Similarly from a security standpoint, if one or more RF tags are
associated with a piece of luggage, detecting a change in the luggage
signature may indicate that the luggage has been opened, which may
indicate that something has been stolen or added to the piece of luggage.
In either instance, further inspection of the luggage may be warranted.
The three dimensional signatures may be used in other applications as
well and the invention is not limited to these several mentioned
applications.

[0035] FIG. 6 shows an embodiment of a reader that may be configured to
obtain RF signatures from a set of RF tags disposed within a volume. As
shown in FIG. 6, responses 60 from tags 10 may be gathered by an antenna
62 and passed to an RF tag reader 64. The antenna may be integrated into
the RF tag reader 64 and the invention isn't limited by the manner in
which the response from the individual RF tags are collected by the RF
tag reader 64.

[0036] The response from the RF tags 52 will be input to processing
circuitry 66 where the tag codes 68 for the various RF tags will be
extracted. In addition, the particular manner in which the RF tags
responded may be stored as an RF signature 70 for the article. The tag
codes and/or signature may be transmitted to a central area for further
processing and/or storage. The invention is not limited by the particular
manner in which these values are used once they have been obtained.
However, as described above, multiple signatures from the same article 50
may be compared over time to determine if the article has been changed in
a way that would change the RF signature of the article.

[0037] The RF tags 52 may be standard RF tags 12 described above in
connection with FIGS. 1-2, or may be RF tags 30 that are configured to
also provide an indication of the electrical characteristics of at least
one of their power coil(s). For example, each RF tag may be configured to
transmit not only its tag code, but also an indication of at least one
electrical characteristic associated with its power coil. This may be
implemented as discussed above in connection with FIGS. 3-4. The relative
power levels of the several RF tags when interrogated from a particular
angle and/or distance may provide information as to whether any of the RF
tags have been moved relative to the location of the RF tag reader, and
thus provide a way for tampering to be detected from an RF tag signature
associated with a given set of RF tags.

[0038] FIGS. 7 and 8 show two processes that may be used to implement
embodiments of the invention. As shown in FIG. 7, power from antennas in
multiple dimensions may be used to power an RF tag (100). The power level
(or other electrical characteristic) from each antenna may then be
transmitted along with the RF tag code to a tag reader (102). The tag
reader or an associated RF tag processing system will interpret the power
levels from the antennas to determine an orientation of the RF tag
relative to the RF tag reader (104). Alternatively, the tag reader may
pass this information back to a central RF tag processing system that may
then interpret the power levels of the antennas to determine the
orientation of the RF tag relative to the RF tag reader. The particular
location where this process happens will depend on how the invention is
implemented and the invention is not to be limited in this manner to any
particular implementation.

[0039] Where the tag reader is mobile, the mobile tag reader may be able
to determine its position based on the orientation information obtained
from a fixed RF tag (106). Similarly, where the tag reader is fixed, the
location of the RF tag may be determined by analyzing the power levels
recorded by the RF tag (108). The relative location information may then
be used in many different ways depending on the particular application
being implemented.

[0040] In the process shown in FIG. 8, when an article containing multiple
RF tags enters an EM field associated with a tag reader (110), the RF
tags in the article are powered by the EM field and emit a tag code,
optionally in conjunction with information about the electrical
characteristics of their one or more power coils (112). The combination
of tag codes, the order in which the RF tags respond, the
encrypted/unencrypted nature of the tag codes, and the other
characteristics associated with the transmissions from the RF tags on the
article are used to form a signature for the article as a whole (114).
The RF tag codes may then be compared with expected RF tag codes to
identify the article and to determine whether all of the expected RF tags
have responded (116). The signature may also be checked against a
previous signature for the article to determine if the signature has
changed significantly (118). The signatures for the article may be used
in many different ways as well, depending on the particular application
being implemented.

[0041] FIG. 9 shows a functional block diagram of a RF tag processing
system embodied as a computer system 120 that may be used to enable three
dimensional RF signatures to be used to understand information about
articles associated with the RF tag(s). In the embodiment shown in FIG.
9, the computer system 120 includes one or more input/output ports 122 to
enable RF tag information to be received from one or more RF tag readers.
The input/output ports may be standard network ports configured to enable
the RF tag readers and the RF tag processing system to be interconnected
by a communication network. Alternatively the input/output ports may be
serial ports or other types of ports, for example where the RF tag
reader(s) are directly connected to the computer system. Although the
embodiment shows the computer system as separate from the RF tag readers,
alternatively the processing functions described in connection with FIG.
9 may be performed by processing circuitry integrated with one or more of
the RF tag readers. Thus, part of the functionality described as being
attributable to the RF tag processing system may be distributed and
instantiated in the RF tag reader or another component associated with
the RF tag processing system. Similarly, some of the processing may be
implemented on the RF tags themselves, particularly in connection with
the three dimensional RF tags, and the invention is not limited to an
embodiment in which all of the processing is done in the precise manner
described herein.

[0042] The computer system includes a processor 124 containing control
logic 126 configured to enable the processor to perform the functions
associated with the RF tag processing system described herein.
Specifically, the control logic may be connected to a memory 128
containing software and/or data that will enable the computer system to
process RF tag responses, individually and collectively, to enable three
dimensional information to be extracted from the RF tag responses.

[0043] In the embodiment shown in FIG. 9, the memory 128 includes RF tag
software 130 enabling the RF processing system to maintain a correlation
between RF tags and the articles with which they are associated. Many
commercial systems have been developed to track articles using RF tags,
and the RF tag software 128 in FIG. 9 may be configured to implement
article tracking features in a manner similar to one or more of these
commonly available systems. For example, the RF tag software may access a
database of RF tags 132 and associated articles so that the system may
provide information associated with particular articles to an operator of
the RF processing system. Similarly, the RF tag software may have access
to a database of RF tag readers 134 to determine the physical location of
the readers that are providing RF tag information to the RF tag
processing system.

[0044] The RF tag processing system shown in FIG. 9 also includes multiple
power coil RF tag direction determination software 136. The software 136
may be a software module that is incorporated into the RF tag software
130 or may be a stand-alone software program. The software 136 may be
configured to perform the process shown in FIG. 7 and described in
greater detail in connection with FIGS. 3-4. In connection with this, the
software 136 may access the RF tags database 132 to obtain characteristic
and/or calibration information for particular tags, and may also access
the RF tag reader information database 134 to obtain information about
particular RF tag readers so that it can determine how the power coil
information should be interpreted for a particular RF tag and with
reference to the particular RF tag reader that registered the RF tag
response.

[0045] The RF tag processing system may also include multiple RF tag
article signature software 138 which, like the software 136, may be
incorporated into the RF tag software 130 or may be a stand-alone
software program. The software 138 may be configured to perform the
process shown in FIG. 8 and described in greater detail in connection
with FIGS. 5-6. In connection with this, the software 138 may be
configured to receive RF tag signature information associated with an
article, or to create a RF tag signature from multiple RF tags associated
with a given article, and optionally then to compare the RF tag signature
with a previous RF tag signature for the article. RF tag signatures from
combinations of RF tags associated with a given article may be stored in
an article signatures database 140 to enable different signatures for the
same article to be compared at different points in time to detect
tampering with the article.

[0046] The control logic 126 may implement one or more processes in
addition to those shown here, or as an alternative to those shown here,
to enable the computer system to implement an RF tag processing system
that can generate and/or use three dimensional RF tag signatures. Many
other standard components of the computer system have not been
illustrated to avoid obfuscation of the more relevant aspects. As is well
known in the art, a complete computer system will include many additional
components that have not been shown here.

[0047] The functions described above may be implemented as a set of
software program instructions that are stored in a computer readable
memory and executed on one or more processors. However, it will be
apparent to a skilled artisan that all logic described herein can be
embodied using discrete components, integrated circuitry such as an
Application Specific Integrated Circuit (ASIC), programmable logic used
in conjunction with a programmable logic device such as a Field
Programmable Gate Array (FPGA) or microprocessor, a state machine, or any
other device including any combination thereof. Programmable logic can be
fixed temporarily or permanently in a tangible medium such as a read-only
memory chip, a computer memory, a disk, or other storage medium.
Programmable logic can also be fixed in a computer data signal embodied
in a carrier wave, allowing the programmable logic to be transmitted over
an interface such as a computer bus or communication network. All such
embodiments are intended to fall within the scope of the present
invention.

[0048] It should be understood that various changes and modifications of
the embodiments shown in the drawings and described in the specification
may be made within the spirit and scope of the present invention.
Accordingly, it is intended that all matter contained in the above
description and shown in the accompanying drawings be interpreted in an
illustrative and not in a limiting sense. The invention is limited only
as defined in the following claims and the equivalents thereto.